Colorists to the stars tell us which blondes, brunettes, redheads and raven-haired ladies in Hollywood have the most beautiful hair color -- and how you can copy it

Why it works:
"The beauty of their hair is that even though they are light blonde, their hair still looks healthy and shiny. Light blonde hair can tend to look over processed and has a damaged, dull, ashy tone to it if it isn't lightened carefully. On the other end, some hair, if too warm or gold, can clash with skin tones and look brassy," says John.